Many bioactive metabolites possess unusual carbohydrates required for molecular recognition. (See for example, Liu, H.-w.; Thorson, J. S. Ann. Rev. Microbiol., 1994, 48, 223-256; Weymouth-Wilson, A. C. Nat. Prod. Rep. 1997, 14, 99-110; In Macrolide Antibiotics, Chemistry, Biology and Practice; Omura, S. Ed., Academic Press: New York; 1984; Johnson, D. A.; Liu, H.-w. Curr. Opin. Chem. Biol. 1998, 2, 642-649; and Trefzer, A.; Salas, J. A.; Bechthold, A. Nat. Prod. Rep. 1999, 16, 283-299.) In fact, roughly 70% of current lead compounds in modern drug discovery derive directly from natural products, many of which are glycosylated metabolites. (See Thorson, J. S. et al. Nature's Carbohydrate Chemists: The Enzymatic Glycosylation of Bioactive Bacterial Metabolites. Curr. Org. Chem. manuscript in press, (2000); and references therein and Weymouth-Wilson, A. C. The Role of Carbohydrates in Biologically Active Natural Products. Nat. Prod. Rep. 14, 99-110 (1997)). Examples of pharmaceutically important glycosylated metabolites include, for example, amphotericin, megalomicin/erythromycin, mithramycin, doxorubicin, vancomycin and calicheamicin, as shown in FIG. 5. While it is known that the sugar moieties of these pharmaceutically important metabolites often define their corresponding biological activity, (see Weymouth-Wilson, A. C., The Role of Carbohydrates in Biologically Active Natural Products, Nat. Prod. Rep. 14, 99-110 (1997)), efficient methods to systematically alter these essential carbohydrate ligands are still lacking.
In metabolite biosynthesis, glycosylation begins with the nucleotidylyltransferase-catalyzed activation of a sugar phosphate as a nucleotide diphosphosugar (NDP-sugar) donor. After activation, a number of enzymatic processing reactions often occur (e.g., deoxygenation, transamination, oxidation/reduction, epimerization, alkylation, and decarboxylation) prior to the culminating glycosyltransferase-catalyzed attachment to the aglycon. (Liu, H.-w. & Thorson, J. S. Pathways and Mechanisms in the Biogenesis of Novel Deoxysugars by Bacteria. Ann. Rev. Microbiol. 48, 223-256 (1994); Kirschning, A., Bechtold, A. F-W. & Rohr, J. Chemical and Biochemical Aspects of Deoxysugars and Deoxysugar Oligosaccharides. Top. Curr. Chem. 188, 1-84 (1997); Johnson, D. A. & Liu, H.-w. Mechanisms and Pathways from Recent Deoxysugar Biosynthesis Research. Curr. Opin. Chem. Biol. 2, 642-649 (1998); Hallis, T. M. & Liu, H.-w. Learning Nature's Strategies for Making Deoxy Sugars: Pathways, Mechanisms, and Combinatorial Applications. Acc. Chem. Res. 32, 579-588 (1999); Johnson, D. A. & Liu, H.-w. In Comprehensive Chemistry of Natural Product Chemistry (Barton, D.; Nakanishi; K.; Meth-Cohn, O. eds), Elsevier Science, Oxford, 311, (1999); Trefzer, A., Salas, J. & Bechthold, A. Genes and Enzymes Involved in Deoxysugar Biosynthesis in Bacteria. Nat. Prod. Rep. 16, 283-299 (1999); and Bechthold, A. & Rohr, J. In New Aspects of Bioorganic Chemistry (Diederichsen, U.; Lindhorst, T. K.; Wessjohann, L.; Westerman, B., eds.) Wiley-VCH, Weinheim, 313, (1999)).
The glycosyltransferases that incorporate these essential ligands are thought to rely almost exclusively upon UDP- and TDP-nucleotide sugars; however some have demonstrated promiscuity towards the sugar donor, (e.g., Gal, D-galactose; Glc, D-glucose; Man, D-mannose; NTP, nucleotide triphosphate; pFPTC, pentafluorophenoxythiocarbonyl; TDP, thymidine diphosphate; TMP, thymidine monophosphate; TTP, thymidine triphosphate; UDP, uridine diphosphate.) Genetic experiments suggest that downstream glycosyltransferases in secondary metabolism are promiscuous with respect to their NDP-sugar donor, setting the stage for the expansion of “combinatorial biosynthesis” approaches to change metabolite glycosylation. (See Madduri, K. et al., Production of the antitumor drug epirubicin (4′-epidoxorubicin) and its precursor by a genetically engineered strain of Streptomyces peucetius Nat. Biotech. 16, 69-74 (1998); and Hutchinson, C. R. Combinatorial Biosynthesis for New Drug Discovery. Curr. Opin. Microbiol. 1, 319-329 (1998).) This information has led to the exploitation of the carbohydrate biosynthetic machinery to manipulate metabolite glycosylation, (Madduri, K.; Kennedy, J.; Rivola, G.; Inventi-Solari, A.; Filppini, S.; Sanuso, G.; Colombo, A. L.; Gewain, K. M.; Occi, J. L.; MacNeil, D. J.; Hutchinson, C. R. Nature Biotech. 1998, 16, 69-74; and Zhao, L.; Ahlert, J.; Xue, Y.; Thorson, J. S.; Sherman, D. H.; Liu, H.-w. J. Am. Chem. Soc., 1999, 121, 9881-9882 and references therein), revitalizing interest in methods to expand the repertoire of available UDP- and TDP-sugar nucleotides. (See Zhao, Y.; Thorson, J. S. J. Org. Chem. 1998, 63, 7568-7572; and Elhalabi, J. M.; Rice, K. G. Cur. Med. Chem. 1999, 6, 93-116.)
These in vivo methods are limited by both a particular host's biosynthetic machinery and the specific host's tolerance to each newly constructed metabolite. Further, in vitro progress in this area is limited by the availability of the required NDP-sugar substrates. (Solenberg, P. J. et al., Production of Hybrid Glycopeptide Antibiotics in vitro and in Streptomyces toyocaensis. Chem. & Biol. 4, 195-202 (1997).)
Thus, there is a need for a greater variety of available NDP-sugar substrates.
Salmonella enterica LT2 α-D-glucopyranosyl phosphate thymidylyltransferase (Ep) is a member of the prevalent nucleotidylyltransferase family responsible for the reversible conversion of α-D-hexopyranosyl phosphate and NTP to the corresponding NDP-sugar nucleotide and pyrophosphate. Of the many nucleotidylyl-transferases studied, the NDP-sugar nucleotide-forming thymidylyltransferases have received the least attention in prior work. (See Lindquist, L.; Kaiser, R.; Reeves, P. R.; Lindberg, A. A. Eur. J. Biochem. 1993, 211, 763-770, and Gallo, M. A.; Ward J.; Hutchinson, C. R. Microbiol. 1996, 142, 269-275.) Even in Ep, substrate specificity studies prior to the work of the present inventors were limited to only a few available hexopyranosyl phosphates. (See Lindquist, L.; Kaiser, R.; Reeves, P. R.; Lindberg, A. A. Eur. J. Biochem. 1993, 211, 763-770.)